Electrodeposited tin/lead alloys of different compositions are valuable in a number of applications including the provision of bearing contact surfaces (for which a 7/93 tin/lead alloy is typically used) and the provision of surfaces for soldering such as on printed circuit boards and the like (for which alloys of 60/40 tin/lead are desired). Although a number of formulations have been suggested for use in producing solder plate, it is believed that a significant need remains for a bath that is capable of producing a high quality tin/lead deposit having a composition at or near the eutectic value for the alloys (about 63/37), as is optimum for soldering purposes. Moreover, effective compositions for producing bright or semi-bright alloy electrodeposits have not been available commercially, and there is a widespread demand for a practical way of producing such deposits on articles of various types for both technical and also aesthetic reasons. It is also desirable that such deposits retain their solderability over extended periods of time, and either be resistant to discoloration or be adapted to facile treatment to prevent such discoloration.
Accordingly, it is an object of the present invention to provide a novel electroplating bath that is capable of producing relatively bright deposits of tin/lead alloy.
It is also an object of the invention to provide such a bath that is capable of producing the metal deposits with good current efficiency, that is operable over a broad range of current densities and that exhibits good covering power.
Another object is to provide workpieces having an optimum tin/lead alloy electrodeposit for soldering, where the composition is at or near the eutectic point for tin/lead alloys and is at least relatively bright.
Still another object is to provide an electroplating method for the production of high quality tin/lead alloy deposits, which method is efficient and effective, is conducted under convenient conditions, and is capable of producing bright solderplate deposits.